Durable Noniridescent Structural Colors Enabled by Ultrafast Infiltration-Assisted Assembly of Hard Core–Soft Shell Nanospheres

Infiltration-assisted (IFAST) colloidal assembly is well compatible with the traditional printing technology and able to rapidly fabricate amorphous photonic crystal (APC) patterns with noniridescent structural colors on permeable substrates such as paper. This technology does not involve any organic solvent and conventional dyes/pigments and hence is regarded as a green printing technology. However, the manufacture of high-quality APC patterns via IFAST assembly remains a significant challenge due to the difficulty of balancing the contradiction between the structural color and mechanical stability, thereby limiting their extensive applications. In this study, a series of monodisperse core–shell nanospheres containing a hard polystyrene (PS) core and soft polyacrylate (PA) shell (with different shell thickness and glass transition temperature (T_g) values) have been successfully synthesized and then directly used to fabricate APC patterns via the ultrafast IFAST assembly approach at room temperature. The influence of shell thickness and T_g on the microstructure, structural color, and mechanical stability of APC patterns was investigated in detail. With the shell thickness increasing or shell T_g falling, the conglutination and fusion between nanosphere shells became remarkable; as a result, the mechanical stability of the colloidal array was gradually enhanced, but the structural color was deteriorated due to its reduced order degree and refractive index (RI) contrast. After controlling the suitable shell thickness and T_g, partial conglutination between these PS@PA nanospheres occurred, and hence, enough RI contrast and short-range ordered structure were successfully retained. Eventually, various APC patterns with both vivid structural color and good mechanical stability were rapidly fabricated by IFAST coassembly. In short, this methodology opens a path for high-speed, facile, and environmentally friendly printing of vivid and firm APC patterns on permeable substrates.